The present invention relates to a method for manufacturing a semiconductor device such as a DRAM including a plurality of MOSFET, particularly to a method for forming a contact hole through an inter-layer insulating layer.
A semiconductor element, such as a Metal-Oxide-Semiconductor Field Effect transistor (xe2x80x9cMOSFETxe2x80x9d) formed on a semiconductor substrate, is covered by an inter-layer insulating layer such as a silicon oxide layer. The inter-layer insulating layer has a contact hole perforated in the direction of thickness of the inter-layer insulating layer. The contact hole is filled with conductive material that makes an electric contact of the semiconductor element with a conductive layer over the inter-layer insulating layer.
Conventional methods for forming the above-mentioned contact hole include so-called Self-Aligned Contact (xe2x80x9cSACxe2x80x9d) method. According to an example of the conventional SAC method, a silicon nitride (SiN) layer is first formed to cover sidewall of the gate of the transistor. Then, an inter-layer insulating layer is formed on the silicon nitride layer. Because of the difference of etching rates, the silicon nitride layer functions as an etch-stopping layer. Therefore by etching the inter-layer insulating layer, a contact hole is formed on a portion of the inter-layer insulating layer under which the silicon nitride layers are not formed.
However, according to the conventional SAC method, it is required to perform process steps for forming the silicon nitride layer and patterning the silicon nitride layer. Therefore, forming a contact hole as a whole includes complicated process steps, and manufacturing cost for a semiconductor device is increased.
Therefore, the present invention provides a method for manufacturing a semiconductor device by forming a contact hole through simplified process steps.
The present invention may be achieved by using a low pressure chemical vapor deposition (xe2x80x9cLPCVDxe2x80x9d) method for forming an inter-layer insulating layer with tetramethylcyclotetrasiloxane ([SiH(CH3)]4O4) as a source gas and oxygen gas as an annexation gas under vacuum ultraviolet light.
Basically, the method for manufacturing a semiconductor device of the present invention includes a process step for forming a contact hole, which perforates through an insulating layer in the direction of thickness of the insulating layer. The insulating layer is formed to cover conductors spaced apart from one another and formed on the surface of the semiconductor substrate. In order to form the insulating layer, tetramethylcyclotetrasiloxane ([SiH(CH3)]4O4) as a source gas and an oxygen gas as an adjunction gas are provided into a reaction chamber of a LPCVD apparatus where the semiconductor substrate is placed. Then, the insulating layer is formed under vacuum ultraviolet light illuminating the semiconductor substrate.
By forming the insulating layer according to the method described above, the insulating layer has a surface profile corresponding to a convex and concave profile of the conductors on the semiconductor substrate. Further portions of the insulating layer, corresponding to the surface portions of the semiconductor substrate are formed to be relatively thin. Therefore, by etching the whole insulating layer, the relatively thin portions of the insulating layer is removed. That is, a contact hole is formed through the insulating layer without performing conventional process steps, such as forming a silicon nitride layer and patterning the silicon nitride layer.
The process step for etching the insulating layer may preferably be a step for performing a dry etching almost uniformly on the overall surface of the insulating layer, so that the relatively thin portions can be removed without damaging other portions. Further, as described above, since it is possible to perform a xe2x80x9cblanketxe2x80x9d dry etching, there is no need to use an etching mask for forming a contact hole.